A telecommunication network power system usually includes an ac-dc stage converting the power from the ac utility line to a 48V dc distribution bus and a dc-dc stage converting the 48V dc distribution bus to a plurality of voltage levels for all types of telecommunication loads. Alternatively, the 48V dc distribution bus may be converted into a low voltage bus through an isolated dc-dc converter. Furthermore, a plurality of downstream non-isolated dc-dc converters with inputs coupled to the low voltage bus may generate a variety of voltage levels in accordance with the needs of the telecommunication network power system. Usually, the dc distribution bus may have a relatively wide voltage rang. For example, the dc distribution bus may have a range from 36V to 75V in a normal operation mode. During a transient, the dc distribution bus' transient voltage is usually up to 100V.
To achieve an optimized distributed power system, one or more non-isolated power converters may be used to reduce the range variation of the distribution bus voltage. The non-isolated dc-dc converters can be implemented by using different power topologies, such as buck dc-dc converters, boost dc-dc converters, buck-boost dc-dc converters, linear regulators and/or the like.
In order to have a reliable telecommunication power system, a variety of protection devices may be connected in series with non-isolated dc-dc converters to form non-isolated dc-dc regulators. For example, an inrush current limiting device such as an n-type metal oxide semiconductor (NMOS) transistor may be placed between an input voltage bus and a buck dc-dc converter. When the buck dc-dc converter is plugged into the input voltage bus, the inrush current limiting device helps to reduce the current flowing into the dc-dc converter by slowly turning on the NMOS transistor. Likewise, a reverse polarity protection device may be connected in series with a dc-dc converter. The reverse polarity protection device helps to prevent a current flowing into the dc-dc converter when reverse polarity occurs. Conventionally, these protection switches are placed in the main power path of the dc-dc converter. As a result, the protection switches may endure full voltage and current stresses of the dc-dc converter. Such full voltage and current stresses may cause extra power losses in the dc-dc converter.